It remained unclear Thursday night what caused the succession of explosions across the Merrimack Valley, but the sporadic fires in Lawrence, Andover, and North Andover were likely the result of excess amounts of natural gas coursing through the region’s old pipes, some of which were being upgraded this week.

Officials at Columbia Gas, which provides natural gas to most residents in the region, said in a statement on Thursday that they would be working on their pipelines in the area to improve reliability and add safety features.

But officials at the utility, which is owned by the Indiana-based NiSource Inc., declined to comment on the cause of the explosions.

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“We’re still gathering information,” said Ken Stammen, a spokesman for the company.

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In a statement, he added: “The first priority for our crews at the scene is to ensure the safety of our customers and the community by supporting first responders and completing safety checks on our system and in the surrounding area.”

At a news conference shortly before 9 p.m., about four hours after the fires started, Andover Fire Chief Michael Mansfield said he had not received a call or an explanation from Columbia about the cause of the explosions.

“It looked like Armageddon,” he said. “I’ve been in the fire service for 39 years; I’ve never seen anything like this in my entire career.”

He said there had been 38 active fires and an additional 17 gas leaks had been reported in Andover.

Asked about the cause, Baker said: “That’s one of those questions we’ll solve once we deal with all the public safety issues.”

The governor called Columbia Gas’s response “adequate.”

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“The grade so far is incomplete,” he added.

Those familiar with the natural gas industry said the cause of the explosion was likely the result of the over pressurization of the gas lines.

It was unclear whether that was the result of a failure of equipment, some kind of human error, or an intentional act.

“There’s no question that there was over-pressurization,” said Mark McDonald, president of NatGas Consulting, a Boston company that investigates gas explosions. “The question is how it happened.”

Natural gas comes to communities throughout the state via high-pressure mains, often at around 60 pounds of pressure per square inch. From there, it’s routed through a substation that reduces the pressure to about a quarter of a pound per square inch.

The reason some houses remained intact while others ignited was likely because of the volatile nature of the gas, he and others said.

Too much gas would make it unlikely to be flammable, as well as too little. To cause a fire, just the right amount of gas is required, as well as some kind of ignition source, which could be a light switch, a water heater, or even a telephone call.

“If you have the right amount of gas, every pilot light could become a blow torch,” said Bob Ackley, president of Gas Safety USA, a leak-monitoring company in Southborough.

He said it was possible that a utility crew working in the area could have connected the wrong pipes, transferring the high pressure main into a low-pressure pipe that feeds directly into homes.

A similar incident occurred in Lexington in 2005, when KeySpan workers received an erroneous work order that caused a crew to connect a high-pressure gas line to a low-pressure line, triggering the destruction of one house and near-explosions at seven others.

Six years ago in Springfield, a gas leak explosion from another Columbia Gas main leveled a strip club and injured 21 people. That was the result of a worker puncturing a gas line with a tool.

As of the end of 2017, the state’s utilities reported nearly 16,000 gas leaks throughout Massachusetts, down from 20,000 in 2015. Only a small number of those are considered enough of a danger that they could be flammable.

Last year, Columbia Gas acquired new technology to help their crews detect and plug leaks along its 5,000 miles of pipelines in Massachusetts. The company last year reported about 3,000 known leaks in its system.

The state has required the utilities to reduce their leaks, and in recent years, they have been spending tens of millions of dollars to upgrade their pipes.

Still, Audrey Schulman, president of the Home Energy Efficiency Team, a Cambridge nonprofit that has mapped tens of thousands of gas leaks around the state, said the explosions are a symptom of a larger problem.

“It’s crazy that in order to cook our food and get heat, we bring an explosive substance into our homes and light it on fire,” she said. “We forget how dangerous it is.”